Cork-Derived Carbon Sheets for High-Performance Na-Ion Capacitors

[Image: see text] S-doped carbon sheets have been easily prepared by deconstructing the 3D cellular structure of a fully sustainable and renewable biomass material such as cork through a mild ball-milling process. S-doping of the material (>14 wt % S) has been achieved by using sulfur as an earth-abundant, cost-effective, and environmentally benign S-dopant. Such synthesized materials provide large Na storage capacities in the range of 300–550 mAh g(–1) at 0.1 A g(–1) and can handle large current densities of 10 A g(–1), providing 55–140 mAh g(–1). Their increased packing density compared to the 3D pristine structure allows them to also provide good volumetric capacities in the range of 285–522 mAh cm(–3) at 0.1 A g(–1) and 53–133 mAh cm(–3) at 10 A g(–1). In addition, highly porous carbon sheets (S(BET) > 2700 m(2) g(–1)) have been produced from the same carbon precursor by rationally designing the chemical activation approach. These materials are able to provide good anion storage capacities/capacitances of up to 100–114 mAh g(–1)/163–196 F g(–1). A sodium-ion capacitor assembled with the optimized S-doped carbon sheets and the highly porous carbon sheets with mass matching ratios provided the best energy/power characteristics (90 Wh kg(–1) at 29 kW kg(–1)) in combination with robust cycling stability over 10,000 cycles, with a capacity fade of only 0.0018% per cycle.